1. Field of the Invention
The present invention relates generally to power control in a mobile communication system, and more particularly, to an apparatus and method for signaling of a transmitting end and estimation of a receiving end, whereby the transmitting end of a mobile communication system controls transmit power between physical layers so that the receiving end may effectively estimate the transmit power between the physical layers.
2. Description of the Related Art
Mobile communication systems are evolving from voice-oriented services to high speed, high volume services such as data services, multimedia services, etc.
Recent mobile communication systems employ standards using an Adaptive Modulation and Coding (AMC) scheme in which a modulation order and a coding rate are regulated according to a wireless channel condition in order to achieve high-speed data transmission within a limited frequency band.
The AMC scheme has a plurality of combinations of modulation orders and coding rates. In general, the combinations of modulation orders and coding rates are referred to as a Modulation and Coding Scheme (MCS).
The AMC scheme may improve spectral efficiency by determining and transmitting an MCS level according to a channel condition between a User Equipment (UE) and a Base Station (BS) currently connected to the UE.
When using the AMC scheme, if the channel condition between the UE and the BS is excellent, an MCS for a high-order modulation scheme (e.g., 8-Phase-Shift Keying (PSK), 16-Quadrature Amplitude Modulation (QAM), 64-QAM, etc.) is selected. Otherwise, if the channel condition between the UE and the BS is poor, an MCS for a low-order modulation scheme (e.g., Binary Phase-Shift Keying (BPSK) or Quadrature Phase-Shift Keying (QPSK)) is selected.
BPSK, which is one of the low-order modulation schemes, may generate a Log Likelihood Ratio (LLR) to be delivered to a channel decoder for each symbol on a constellation, in the presence of phase information of a channel, without having to use additional information. For general use of a Max-Log-MAP scheme, QPSK also may generate the LLR, in the presence of the phase information of the channel, without having to use additional information.
However, even when using the Max-Log-MAP scheme, 8-PSK, 16-QAM, and 64-QAM schemes require information on a phase and size of the channel to generate the LLR.
A mobile communication system, which requires such channel information, estimates a channel by receiving a signal with a predetermined format to estimate the channel information. The signal transmitted for channel estimation is referred to as a pilot signal.
In general, the pilot signal used for channel estimation is a common pilot signal that may be received by all user terminals for the effective use of radio frequency resources. A dedicated pilot signal may be transmitted for a specific user terminal.
In order for a channel estimation result to be used for demodulation and LLR generation, there is a need to know a power ratio (or a symbol energy ratio) between a pilot signal and other signals of physical channels for which demodulation and LLR generation are necessary. This is requirement is due to the fact that power for guaranteeing quality of the physical channels is generally different from power for guaranteeing quality of the pilot signal.
A high volume mobile communication system is implemented by using a high-order modulation scheme. Since a power ratio between a pilot signal used for channel estimation and a traffic signal is different, information on the power ratio between the pilot signal and the traffic signal is required for demodulation and LLR generation.
In delivering the power ratio from a transmitting end to a receiving end using signaling, a signaling overhead increases. Further, if the receiving end estimates the power ratio, a traffic error rate may increase due to erroneous estimation.
In particular, it is difficult to estimate the power ratio when using a Spatial Multiplexing Multiple Input Multiple Output (SM MIMO) system, which has recently been used to increase spectral efficiency.